Roberto Lampariello

Trajectory planning for optimal robot catching in real-time

Many real-world tasks require fast planning of highly dynamic movements for their execution in real-time. The success often hinges on quickly finding one of the few plans that can achieve the task at all. A further challenge is to quickly find a plan which optimizes a desired cost. In this paper, we will discuss this problem in the context of catching small flying targets efficiently. This can be formulated as a non-linear optimization problem where the desired trajectory is encoded by an adequate parametric representation. The optimizer generates an energy-optimal trajectory by efficiently using the robot kinematic redundancy while taking into account maximal joint motion, collision avoidance and local minima. To enable the resulting method to work in real-time, examples of the global planner are generalized using nearest neighbour approaches, Support Vector Machines and Gaussian process regression, which are compared in this context. Evaluations indicate that the presented method is highly efficient in complex tasks such as ball-catching.

Robot excitation trajectories for dynamic parameter estimation using optimized B-splines

In this paper we adressed the problem of finding exciting trajectories for the identification of manipulator link inertia parameters. This can be formulated as a constraint nonlinear optimization problem. The new approach in the presented method is the parameterization of the trajectories with optimized B-splines. Experiments are carried out on a 7 joint Light-Weight robot with torque sensoring in each joint. Thus, unmodeled joint friction and noisy motor current measurements must not be taken into account. The estimated dynamic model is verified on a different validation trajectory. The results show a clear improvement of the estimated dynamic model compared to a CAD-valued model.

Impedance Control for a Free-Floating Robot in the Grasping of a Tumbling Target with Parameter Uncertainty

This paper addresses an impedance control for a free-floating space robot in the grasping of a tumbling target with model uncertainty. Firstly, the operational space dynamics for a free-floating robot is derived with a novel, computationally efficient formulation. Then, considering the grasped target as a disturbance force on the end-effector, the proposed control method is completely independent of the target inertial parameters and the end-effector can follow a given trajectory in the presence of model uncertainty. To verify the effectiveness of the proposed method, a three-dimensional realistic numerical simulation is carried out

Generating feasible trajectories for autonomous on-orbit grasping of spinning debris in a useful time

The grasping and stabilization of a spinning, noncooperative target satellite by means of a free-flying robot is addressed. A method for computing feasible robot trajectories for grasping a target with known geometry in a useful time is presented, based on nonlinear optimization and a look-up table. An off-line computation provides a data base for a mapping between a four-dimensional input space, to characterize the target motion, and an N-dimensional output space, representing the family of time-parameterized optimal robot trajectories. Simulation results show the effectiveness of the data base for computing grasping maneuvers in a useful time, for a sample range of spinning motions. The debris object consists of a satellite with solar appendages in Low Earth Orbit, which presents collision avoidance and timing challenges for executing the task.

Optimal motion planning for free-flying robots

This paper addresses the problem of motion planning for free-flying robots. Full state actuation is considered to allow for large displacements of the spacecraft. Motion planning is formulated as an optimization problem and kinematic as well as dynamic constraints are considered. The chosen optimization criteria are spacecraft actuation and final time. The proposed method allows solutions which do not require any spacecraft actuation for those end goals for which the robot motion is sufficient.

Advances in orbital robotics

Outlines the situation in orbital space robotics with special reference to what DLR (German Aerospace Center) has contributed to the field. After our ROTEX experiment, the first remotely controlled space robot inside the space shuttle, the Japanese ETS VII has now been the first remotely controlled free-flying space robot. We had the opportunity to control this arm from the ground, too, including the use of the robot arm as a satellite attitude controller. It is outlined how it is now time to take the next steps towards operational ground-controlled space robot systems, presumably first on the International Space Station, but later on as free flying robonauts assisting or even replacing extra vehicular activities.

A Differentially Flat Open-Chain Space Robot with Arbitrarily Oriented Joint Axes and Two Momentum Wheels at the Base

The motion of a free-floating space robot is characterized by the principle of conservation of angular momentum. It is well known that these angular momentum equations are nonholonomic, i.e., are nonintegrable rate equations. If the base of the free-floating robot is partially actuated, it is difficult to determine joint trajectories that will result in point-to-point motion of the entire robot system in its configuration space. However, if the drift-less system associated with the angular momentum conservation equations is differentially flat, point-to-point maneuvers of the free-floating robot in its configuration space can be constructed by properly choosing trajectories in the differentially flat space. The primary advantages of this approach is that it avoids the use of nonlinear programming (NLP) to solve the nonintegrable rate equations, which at best can provide only approximate solutions. A currently open research problem is how to design a differentially flat space robot with under-actuated base. The contributions of this technical note are as follows: i) study systematically the structure of the nonholonomic rate constraint equations of a free-floating open-chain space robot with two momentum wheels at the base and arbitrarily oriented joint axes; ii) identify a set of sufficient conditions on the inertia distribution under which the system exhibits differential flatness; iii) exploit these design conditions for point-to-point trajectory planning and control of the space robot.

The OOS-SIM: An on-ground simulation facility for on-orbit servicing robotic operations

On-orbit servicing involves a new class of space missions in which a servicer spacecraft is launched into the orbit of a target spacecraft, the client. The servicer navigates to the client with the intention of manipulating it, using a robotic arm. Within this framework, this work presents a new robotic experimental facility which was recently built at the DLR to support the development and experimental validation of such orbital servicing robots. The facility allows reproducing a close-proximity scenario under realistic three-dimensional orbital dynamics conditions. Its salient features are described here, to include a fully actuated macro-micro system with multiple sensing capabilities, and analyses on its performance including the amount of space environment volume that can be simulated.

MODELING AND EXPERIMENTAL DESIGN FOR THE ON-ORBIT INERTIAL PARAMETER IDENTIFICATION OF FREE-FLYING SPACE ROBOTS

A method is proposed for the identication of the inertial parameters of a free-ying robot directly in orbit, using accelerometers. This can serve to improve the path planning and tracking capabilities of the robot, as well as its efcienc y in energy consumption. The method is applied to the identication of the base body and of the load on the end-effector, giving emphasis to the experimental design. The problem of the identication of the full system is also addressed in its theoretical aspects. The experience from the Getex Dynamic Motion experiments performed on the ETS-VII satellite have allowed to determine a most suitable model for the identication.

Optimization-based generation and experimental validation of optimal walking trajectories for biped robots

In this paper the generation of walking gaits for biped robots is addressed as a nonlinear optimization problem. The latter presents an efficient formulation, which only requires parameterizing the joint states and does not require to integrate the equations of motion. The results of the optimization are applied to a real robot, with the aid of a suitable stabilizing controller. The final gain in optimized cost is assessed, for the real system. The experimental results confirm the effectiveness of the method.